Spread popcorn onto 2 greased shallow pans, such as jelly roll pans or disposable roasting pans.
Preheat oven to 250. In a large saucepan, combine brown sugar, corn syrup, salt, and butter. Bring to boil over medium heat, stirring until everything is well combined. Boil for 5 minutes, stirring constantly.
Remove from heat and stir in baking soda and vanilla. Immediately pour the caramel over the popcorn, tossing popcorn to coat.
Bake for one hour, removing pans every 15 minutes to toss popcorn.
Melt white chocolate in microwave, microwaving for 30 seconds and then kneading bag or stirring until completely melted. Drizzle over popcorn. Repeat with milk chocolate. Allow to cool and then break into pieces. Store in an airtight container for up to 1 week.